Consolidated Statements Of Changes In Shareholders' Equity - USD ($) shares in Millions, $ in Millions	Total		Nonredeemable Preferred Stock	Common Stock	Capital Surplus	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
BALANCE (in shares) at Dec. 31, 2019				142.1
BALANCE at Dec. 31, 2019	$ 7,327			$ 1,141	$ 2,174	$ (316)	$ 9,619	$ (5,291)
Cumulative effect of change in accounting principle	13						13
Net income	59	[1]					59
Other comprehensive income (loss), net of tax	382					382
Cash dividends declared on common stock	(190)						(190)
Purchase of common stock	(194)							(194)
Purchase of common stock (in shares)				(3.4)
Issuance of preferred stock	395		$ 395
Net issuance of common stock under employee stock plans	(2)				(13)		(5)	16
Net issuance of common stock under employee stock plans (in shares)				0.3
Share-based compensation	12				12
BALANCE at Jun. 30, 2020	7,802		395	$ 1,141	2,173	66	9,496	(5,469)
BALANCE (in shares) at Jun. 30, 2020				139.0
BALANCE (in shares) at Mar. 31, 2020				139.0
BALANCE at Mar. 31, 2020	7,402			$ 1,141	2,168	87	9,476	(5,470)
Net income	118	[1]					118
Other comprehensive income (loss), net of tax	(21)					(21)
Cash dividends declared on common stock	(96)						(96)
Purchase of common stock	(1)							(1)
Issuance of preferred stock	395		395
Net issuance of common stock under employee stock plans	(1)				1		(2)
Share-based compensation	4				4
BALANCE at Jun. 30, 2020	7,802		395	$ 1,141	2,173	66	9,496	(5,469)
BALANCE (in shares) at Jun. 30, 2020				139.0
BALANCE (in shares) at Dec. 31, 2020				139.2
BALANCE at Dec. 31, 2020	8,050		394	$ 1,141	2,185	64	9,727	(5,461)
Net income	678						678
Other comprehensive income (loss), net of tax	(184)					(184)
Cash dividends declared on common stock	(187)						(187)
Cash dividends declared on preferred stock	(11)						(11)
Purchase of common stock	(453)				(24)			(429)
Purchase of common stock (in shares)				(5.9)
Issuance of preferred stock	0
Net issuance of common stock under employee stock plans	9				(27)		(5)	41
Net issuance of common stock under employee stock plans (in shares)				0.6
Share-based compensation	29				29
BALANCE at Jun. 30, 2021	7,931		394	$ 1,141	2,163	(120)	10,202	(5,849)
BALANCE (in shares) at Jun. 30, 2021				133.9
BALANCE (in shares) at Mar. 31, 2021				139.6
BALANCE at Mar. 31, 2021	8,152		394	$ 1,141	2,183	(105)	9,975	(5,436)
Net income	328						328
Other comprehensive income (loss), net of tax	(15)					(15)
Cash dividends declared on common stock	(92)						(92)
Cash dividends declared on preferred stock	(5)						(5)
Purchase of common stock	(450)				(24)			(426)
Purchase of common stock (in shares)				(5.8)
Net issuance of common stock under employee stock plans	6				(3)		(4)	13
Net issuance of common stock under employee stock plans (in shares)				0.1
Share-based compensation	7				7
BALANCE at Jun. 30, 2021	$ 7,931		$ 394	$ 1,141	$ 2,163	$ (120)	$ 10,202	$ (5,849)
BALANCE (in shares) at Jun. 30, 2021				133.9

[1] See Defined Benefit Pension and Other Postretirement Costs in Note 1.